1. Field of the Invention
This invention relates to a production method of a magnetic circuit member employed for a magnetic circuit used for an electronic device and an electric device as represented by an electromagnetic valve or magnetic sensor and so on comprising a core, a yoke portion and a case portion, the magnetic circuit member and an electromagnetic apparatus.
2. Prior Art
A prior art is described by taking a magnetic circuit member of an electromagnetic valve as an example. Up to now, pure iron or a low-carbon steel which is a soft magnetic material has been used as the magnetic circuit member used for a magnetic circuit of the electromagnetic valve.
Further, recently, it is requested that an electromagnetic valve be more responsive to an external magnetic field in order to further improve controllability. Further, the electromagnetic valve is required to greater enhance a linear response of an attracting force to an exciting current applied to an exciting solenoid coil portion of the electromagnetic valve in order to carry out a good control of a flow rate such as an oil amount and so on.
The pure iron or the low-carbon steel which is a soft magnetic material does not approach a final shape (approximate shape to a product) directly and needs to be manufactured to the shape of the magnetic circuit member by cutting and machining from a bar-shaped member. Therefore, wasted material as cutting or machining stock is left and an increase of the material cost is caused. Further, since this material is high-viscosity material, the cutting is not always good and an increase of the cutting cost which is a fair percentage of the manufacturing cost is caused. Further, in case the magnetic circuit member (for example, the yoke portion or a plunger portion of the electromagnetic valve) has a complex shape, the wasted material is further increased and the manufacturing cost is further increased.
Further, in case conventional pure iron or low-carbon steel is used as the material of the magnetic circuit member of an electromagnetic valve having an exciting solenoid coil portion turned on by a pulsed current (100 Hz to 300 Hz, direct current or alternate current), a linear response of an attracting force becomes inadequate. The following is assumed as the leading reason. When the pulsed current (direct current or alternate current) flows in the exciting solenoid coil portion and the pulsed magnetic field is generated, the magnetic permeability of the prior pure iron or low-carbon steel becomes smaller and the magnetic flux density becomes lower. As a result, it becomes difficult to pass the magnetic flux in the magnetic circuit. In other words, when the frequency of the pulsed current (direct current or alternate current) increases, it becomes difficult to pass the magnetic flux inside of the magnetic circuit member and the magnetic flux passes on the front face of the magnetic circuit member. Due to this skin effect, a skin depth in which the magnetic flux passes becomes smaller. Thereby, in the electromagnetic valve, in accordance with the movement of the plunger portion, the magnetic flux concentrates at the end portion of the yoke portion and the saturation of the magnetic flux occurs early. Then, the amount of the magnetic flux passing between the yoke portion and the plunger portion, and the direction of the magnetic vector, change and it is not possible to ensure a stable magnetic characteristic of the magnetic circuit member. Thereby, the response, especially the linear response, decreases.